Full Idea
If classical logic insists that logical consequence is just a matter of the form, we fail to include as valid consequences those inferences whose correctness depends on the connections between non-logical terms (such as 'round' and 'square').
Gist of Idea
Logical consequence isn't just a matter of form; it depends on connections like round-square
Source
Stephen Read (Thinking About Logic [1995], Ch.2)
Book Reference
Read,Stephen: 'Thinking About Logic' [OUP 1995], p.53
A Reaction
He suggests that an inference such as 'round, so not square' should be labelled as 'materially valid'.